Time delay switch of the gaseous electric discharge tube type



June 10, 1958 -ros ETAL 2,838,633

I TIME DELAY SWITCH OF THE GASEOUS ELECTRIC DISCHARGE TUBE TYPE Filed Nov. 5, 1954 aa-g g United States PatentO TIME BELAY SWITCH OF THE GASEOUS ELEC- TRIC DISCHARGE TUBE TYPE Gyiirgy Lakatos, Janos Szab, Gyiirgy Szigeti, and Janos Weiszburg, Budapest, Hungary, assignors to Egyesult lzzoiarnpa es Villamossagi Reszvenytarsasag, Budapest, Hungary Application November 5, 1954, Serial No. 467,124

Claims priority, application Hungary November 11, 1953 11 Claims. (Cl. 200113.5)

This invention relates to switches of the gaseous electric discharge type, used particularly for starting gaseous electric discharge devices such as fluorescent lamps. Such switches generally comprise a hermetically sealed envelope having an ionizable gaseous filling, lead-in conductors extending into said envelope, two main electrodes at least one of which being of the bimetallic type and adapted to make and break an electric contact with the other main electrode upon the action of heat generated by a gaseous discharge and of cooling down, respectively, and at least one auxiliary electrode arranged in direct electrical connection with any one of the main electrodes. The lead-in conductors are connected each to at least one of the main and auxiliary electrodes.

With the hitherto known glow switches of this type the heat for actuating the bimetallic electrode or electrodes is generated by a glow discharge in a gas or a mixture of gases. With the bimetallic electrode or electrodes being heated by the heat of the glow discharge they are deflected towards and, at a predetermined temperature, contact with each other. This contact causes the glow discharge to be interrupted whereby the generation of heat is stopped too. Then, the bimetallic electrode or electrodes are rapidly cooling down so that the main electrodes part from each other. If such switches are used for starting gaseous electric discharge devices such as fluorescent lamps, contacting of the main electrodes of the switch results in closing the heating circult of the thermionic or hot cathodes of the lamp. The heating circuit of the cathodes being closed thereby a current will flow for a determined time to preheat the cathode to a temperature suitable for starting the device. After the lapse of this time the main electrodes of the switch part from each other whereby the heating circuit of the cathodes is interrupted, causing thereby a voltage impulse by the action of a ballast which starts the dis charge in the fluorescent lamp itself.

The duration of contact of the hitherto known glow switches, however, is often considerably less than would be necessary for heating the thermionic cathodes of the device e. g. a fluorescent lamp to a suflicient temperature so that the glow switch has to make several attempts before the lamp is ultimately started. This means that a corresponding number of voltage impulses is applied to the cathodes of the fluorescent lamp by which the latter is subjected to unnecessary strains to the detriment of its life-time.

The main object of the present invention is to provide a switch of the electric gaseous discharge tube type by the use of which the above said disadvantages of the hitherto known glow switches are eliminated and particularly an increased life-time of the operated gaseous discharge device is obtained by decreasing the number of unsuccessful starting attempts.

Another object of the invention consists in decreasing the number of fllckerings of electric gaseous discharge lamps when being started.

A further object of the invention is the avoiding of det- 2,838,633 Patented June 10, 1958 H rimental strains of the cathodes of electric gaseous discharge devices, especially of fluorescent lamps.

The above objects are attained in that the auxiliary electrode or electrodes of the switch arein accordance with the principal feature of the present invention-selected so that by the heat evolved by the same the cooling of the bimetallic main electrode is delayed and the duration between contacting and parting of the main electrodes is increased thereby. Preferably the dimensions, the material as well as the emissive quality of the surface of the auxiliary electrode will be subject of selection. The above said time delay caused by the auxiliary electrode can be achieved on the one hand by the heat of the gaseous discharge between the auxiliary electrode and the opposite main electrode, this gaseous discharge taking place in shunt to the glow discharge between the two main electrodes, and, on the other hand, by the Joule heat generated in the auxiliary electrode itself during operation of the switch. The balance of the above said discharge heat and Joule heat may be chosen in advance even so that one of them is rendered practically insignificant. Thus, the temperature of the auxiliary electrode and thereby the time delay of the switch can be adjusted to the desired values. Moreover, it is possible to raise the temperature of the auxiliary electrode higher than that of the main electrodes in which case its maximum value will be at least 690 C. The auxiliary electrode delivers heat in the process of warming up at least at contacting of the main electrodes to the bimetallic main electrode extending thereby the duration of contact. This is, in many cases, desirable in the operation of such switches, especially when applied for starting electric gaseous discharge devices such as fluorescent lamps of the preheated cathode type.

Other objects, features and advantages of the present invention will be described in closer details by taking reference to the accompanying drawings which show, by way of example, several embodiments thereof. In the drawmgs:

Fig. 1 illustrates an embodiment of the time delay switch incorporated in a tube circuit known per se, the envelope of the switch being shown in section.

Fig. 2 is a similar diagrammatic view of another embodiment.

Fig. 3 represents the sectional view of a detail of Fig. 2.

Figs. 4 to 8 show sectional views of further embodiments of the improved time delay switch.

Like parts are referred to by the same reference numbers throughout the drawings.

Referring to the drawings, the switch shown in Fig. 1 comprises a hermetically sealed envelope 1! having an ionizable gaseous filling, e. g. argon, terminated by a base 11. The latter supports two lead-in conductors l2 and 13 which extend into the envelope lid. The switch is provided with two main electrodes 14 and 15. One of the main electrodes, referred to by reference number 14, is a rod-electrode made of e. g. nickel. The other main electrode, referred to by reference number 15, being formed as a bimetallic electrode is composed of e. g. iron and an alloy of iron and nickel in the usual manner. This bimetallic electrode 15 is adapted to move, upon action of heat towards the other main electrode 14 so as to contact and by cooling down to part with it.

/ Furthermore, the switch comprises an auxiliary electrode of e. g. tungsten arranged in direct electrical connection with the bimetallic main electrode 15 one of its ends being connected to the free end of the' bimetallic electrode 15 and its other ends being fixed in the base 11. The lead-in conductors l2 and 13 are connected to the main electrodes 14 and 15, respectively.

With the represented embodiment the auxiliary electrode 16 is chosen so that its cross section should be smaller than 50% of that of the bimetallic electrode 15 while its length is greater than that of the former. Thus, under similar heating eflects of the glow discharge the auxiliary electrode 16 is heated to a higher temperature than the bimetallic electrode 15. Such a heating takes place when a voltage is applied to the main electrodes 14 and 15 and thereby a glow discharge is established between them. The auxiliary electrode 16 having the same potential as the bimetallic electrode 15, a glow discharge is established in shunt to the glow discharge between the two main electrodes 14 and 15 also between thoauxiliary electrode 16 and its opposite electrode which, in case of the represented embodiment, is the main electrode 14. The glow discharge between the rod electrode 14 and the auxiliary electrode 16 causes a flow of current through the latter by which it is additionally heated. Being made of tungsten, it enhances the emission of electrons at least relatively to the main electrode 15 so that after a while the glow discharge between the auxiliary electrode 16 and the opposite main electrode 14 develops into an arc discharge by which the resistance of the path between the auxiliary electrode and the opposite main electrode 14 becomes considerably less than the resistance of the path between the two main electrodes 14 and 15. Thus, an increasing portion of energy of the gaseous discharge flows through the auxiliary electrode 16 and, at the same time, the glow discharge between the two main electrodes 14 and 15 gradually disappears. The increasing flow of energy results in a considerable amount of Joule heat generated in the auxiliary electrode 16 by its resistance and causes the latter to be heated to a temperature higher than that of the main electrodes 14 and 15 and particularly of the bimetallic electrode 15. With the bimetallic main electrode 15 becoming hotter it is deflected towards the opposite main of the two main electrodes becomes equal and the glow -discharge between them completely extinguished. The

auxiliary electrode 16 being on the same potential as 'the bimetallic main electrode 15, also the arc discharge between the auxiliary electrode 16 and the opposite main electrode 14 becomes extinguished. Thus, cooling down of the bimetallic main electrode 15 and its parting with the opposite main electrode 14 would immediately set in were it not for the elevated temperature of the auxiliary electrode 16 the heat of which causes the temperature of the bimetallic main electrode 15 to further increase and thereby the bimetallic main electrode 15 to stay in its contacting position with respect to the opposite main electrode 14. Obviously, the duration of contact between the two main electrodes 14 and 15 is thus increased and a time delay in their parting with one another obtained which is the main object of the present invention as has been described above.

With the represented embodiment the auxiliary electrode 16 consists of a coil. It may, however, consist, among others, of a simple filament, a coiled coil, a plate, a band, a net or web. The cross section of the auxiliary electrode 16 is to be understood as its electrical conductive cross section which is, in case of a filament, a coil or a coiled-coil the cross section of the filament itself, in case of a plate or band the product of the width and the thickness thereof, and in case of a net or web the sum of the cross sections of the elementary filaments of the net or web.

Fig. 1 shows the switch when applied for starting a gaseous electric discharge device, more particularly a per se known fluorescent lamp 17 the cathodes of which are referred to by reference numbers 18 and 19.

Both

cathodes 18 and 19 are of the hot cathode type and consist of a coiled-coil coated with an electron emissive layer as is known in the art and therefore not represented in the drawing. The cathodes 18 and 19 are connected, on one hand, each to one of the main electrodes 14 and 15 of the switch and, on the other hand, through a ballast 20 and a mains switch 21 to mains 22 and 23, respectively. The lead-in conductors 12 and 13 are connected through a condenser 24 in the usual manner.

Upon closing the mains switch 21, the voltage of the mains 22, 23 appears across the ballast 20, the thermionic cathodes 18 and 1 9 of the fluorescent lamp 17 and the lead-in conductors 12 and 13 upon the main electrodes 14 and 15 of the switch causing thereby the glow discharge to set in, on one hand, between the main electrodes 14 and 15 and, on the other hand, between the auxiliary electrode 16 and the rod-electrode 14 which acts as the opposite electrode for both the bimetallic main electrode 15 and the auxiliary electrode 16. As has been described above, the glow discharge between the opposite electrode 14 and the auxiliary electrode 16 develops into an arc discharge whereby the auxiliary electrode reaches a temperature above that of the other electrodes. With the bimetallic main electrode 15 becoming warm, is deflected towards the opposite electrode 14 so as to finally contact therewith. Then the potentials of the opposite electrode 14 and both electrodes 15 and 16 become equal in consequence whereof the glow discharge between the opposite electrode 14 and the bimetallic electrode 15 as well as the arc discharge between the opposite electrode 14 and the auxiliary electrode 16 is extinguished. Under the action of the heat of the auxiliary electrode 16 the contacting position of the main electrodes 14 and 15 is maintained so that the heating circuit of the thermionic cathodes 18 and 19 of the fluorescent lamp 17 is kept closed for an extended period of time which is sufiicient to preheat the thermionic cathodes 18 and 19 to the temperature at which suflicient quantity of electrons are emitted to support an arc discharge therebetween.

Figs. 2 and .3 show an embodiment with which the above mentioned balance of the discharge heat and the resistance heat is adjusted so that the heating of the auxiliary electrode 16 is effected practically by Joule heat .only. To this purpose the auxiliary electrode 16 is 45.

.of e. g. aluminum oxyde (A1 0 .lead-in conductor 13 supports the auxiliary electrode 16 .instead of the main bimetallic electrode 15 which is fixed coated With an electrically insulating layer 26 consisting Furthermore, the

to the base 11 of the switch. Otherwise, the switch and the heating circuit of the fluorescent lamp 17 is similar to that shown in Fig. 1. a

In contrast to Fig. 1, however, the glow discharge is established only between the two main electrodes 14 and 15. By the heat of the glow discharge the bimetallic main electrode 15 is deflected towards the rod-electrode 14. By contacting of the two main electrodes 14 and 15 the gaseous discharge therebetween is extinguished. Then, the current beginning to flow through the thermionic cathodes 18 and 19 of the fluorescent lamp generates Joule heat in the auxiliary electrode 16 connected in series with the thermionic cathodes 18 and 19. The electric resistance of the auxiliary electrode 16 is selected so that the heat generated therein retards the cooling down of the bimetallic main electrode 15 and thereby delays the breaking of the contact of the main electrodes 14 and 15 as was the case with the previously described embodiment.

The advantage of such an embodiment is that the amount of heat needed for providing the time delay in parting of the main electrodes 14 and 15 with one another can be more exactly adjusted.

If the auxiliary electrode 16 of the embodiment shown in Fig. 2 is 'not'provided with the insulating coating 26, the switch operates before contacting of the main electrodes 14 and 15 in the manner described with reference to Fig. 1 whereas after contacting of the main electrodes 14 and 15 it works like the switch shown in Fig. 2. That is, before contacting of the main electrodes 14 and 15 a glow discharge is setting in, on one hand, between the opposite electrode 14 and the bimetallic electrode 15, and, on the other hand, between the opposite electrode 14 and the auxiliary electrode 16, the latter glow discharge developing into an arc discharge. After contacting, however, the flow of current is, in contradistinction to the embodiment shown in Fig. 1, not interrupted, so that in the auxiliary electrode 16 further amounts of resistance heat are being generated. By means of such an embodiment the advantages of the previously described embodiments can be simultaneously warranted and the successful starting operation of e. g. a fluorescent lamp almost completely ensured. Moreover, the duration of contact may be selected arbitrarily.

With the embodiment shown in Fig. 4 the auxiliary electrode 16 is supported in its whole by the lead-in con doctors 13 and the bimetallic main electrode 15, respectively. Furthermore, the auxiliary electrode 16 is arranged between the two legs of the U-shaped bimetallic main electrode 15. Otherwise, this embodiment is similar to that shown in Fig. 1. Such an arrangement is advantageous insofar as the gas discharge between the opposite main electrode 14 and the auxiliary electrode 16 at least partly surrounds the bimetallic main electrode 15 causing thereby a more energetic heating of the latter. Moreover, the auxiliary electrode 16 being supported by the lead-in conductor 13 and the bimetallic main electrode 1'5, respectively, a separate pin for supporting the auxiliary electrode 16 by means of the base 14 is dispensed with which means two sealings-in instead of three.

In operation, upon impressing a voltage on the main electrodes 1.4 and 15, glow discharge will develop in the above described manner. The bimetallic electrode 15 becomes warm and is deflected towards the opposite main electrode 14. At the same time, the auxiliary electrode 16 reaches a temperature higher than that of the bimetallic electrode 15. Thus, at the contacting position of the main electrodes 14 and 15, the latter is further heated by the heat accumulated in the auxiliary electrode 16 which causes an extension of the time of contact even after the gaseous discharges have been extinguished.

Obviously, the auxiliary electrode 16 may be arranged on the bimetallic main electrode also in such a manner that its distance from the opposite main electrode 14 be the greatest. Such an arrangement likewise enhances the warming up of the bimetallic main electrode 15.

it is also possible to coat both the bimetallic main electrode 15 and/or the auxiliary electrode 16 with substances which are chosen so that the work function of the bimetallic electrode 15 should be higher than the work function of the auxiliary electrode 16. Thus, the temperature difference between both these electrodes will be rendered higher and thus the delay in parting of the main electrodes 14 and 15 with one another further increased. Such an embodiment is illustrated in Fig. 5 where, by way of example, the bimetallic main electrode 15 is coated with a layer 27 of gold whereas the auxiliary electrode 16 is provided with a layer 28 made of at least one of the earth alkaline metals and their oxydes, e. g. barium (Ba) and/or barium o-xyde (BaO), in a manner well known in the art, the auxiliary electrode 16 itself being made of tungsten or molybdenum.

The advantage of coating the bimetallic main electrode 15 and the auxiliary electrode 16 in the above described manner consists in the adjustability of the balance between the amounts of discharge heat to which these electrodes are exposed to during operation of the switch whereby also the delay in parting of the main electrodes with one another is rendered adjustable.

With the above described embodiments only one of the main electrodes was of the bimetallic type. It is, however, possible to form both main electrodes as bimetallic electrodes in which case they have to be arranged so as to be deflected towards each other upon heating. With such an arrangement at contacting of the main electrodes, the heat content of the auxiliary electrode is transferred to both of them and breaking of their contact is efliciently delayed.

Moreover, it is possible to provide each bimetallic main electrode with an auxiliary electrode in which case an additional delaying action can be obtained. Such an embodiment is illustrated in Fig. 6.

Both main electrodes 14 and 15 are of the bimetallic type. The main electrodes 14 and 15 are associated each with an auxiliary electrode 29 and 16, respectively.

Upon heating, the bimetallic main electrodes 14 and 15 are deflected towards each other in the manner described with respect to the bimetallic electrode 15' of the embodiment shown in Fig. 1.

he advantage of applying electrodes of the bimetallic type for both main electrodes which is otherwise known in the art is that the time prior to contacting of the main electrode can be shorter. Moreover, both main electrodes may be heated to a relatively lower temperature and the desired inventive action of the auxiliary electrode is more readily obtainable.

Fig. 7 shows an embodiment in which the auxiliary electrode 16 is, contrary to the previously described embodiments, associated with a rod-electrode 14 instead of being associated with a bimetallic electrode 15. The advantage of this embodiment is that the auxiliary electrode 16 is associated with an immovable main electrode 14 e. g. of the rod type and thus relieved from the movements of the bimetallic main electrode 15 whereby its life-time is suitably increased.

A further embodiment of the switch is represented in Fig. 8. In this case the bimetallic main electrode 15 is U-shaped and the auxiliary electrode 16 partly supported by the base 11 is arranged between the legs of the former. The other main electrode 14 is of the known rod type and also has an auxiliary electrode 29 associated therewith. Obviously, the bimetallic main electrode 15 is subject to the heating action of both electrodes 16 and 29 without the auxiliary electrode 29 being compelled to follow the sideways motion of the former. Yet, the additional heat content of the immovable auxiliary electrode 29 is transferred to the bimetallic main electrode 15 when the two main electrodes 14 and 15 contact with one another so that the heating effect of the auxiliary electrode 29 then acts directly upon the bimetallic main electrode 16 and additionally increases the delay of parting of the main electrodes 14 and 15 with one another.

What we claim is:

l. A thermal time delay switch of the gaseous electric discharge type, comprising a hermetically sealed envelope containing an ionisable gas, lead-in conductors extending into said envelope and directly connected each to one of two main electrodes, at least one of said main electrodes being of the bimetallic type and adapted to contact and part with the other of said main electrodes upon the action of heat generated by a gaseous discharge and of cooling down, respectively; at least one auxiliary electrode arranged in direct electrical and thermal connection with a bimetallic main electrode at one of its ends, but being in no direct thermal and electrical connection with said bimetallic main electrode at any intermediate point of said auxiliary electrode, said auxiliary electrode having a metallic surface devoid of any electron-emitting coating comprising a non-metallic substance and being arranged so as to ensure that after having been heated by said gaseous discharge said auxiliary electrode delays the cooling of said bimetallic main electrode, after said bimetallic main electrode has contacted with said other main electrode, by transmitting heat accumulated in said auxiliary electrode to said bimetallic main electrode and thereby increases the dura tion of the electric contact between said main electrodes; said auxiliary electrode being arranged and connected otherwise than in series to said bimetallic main electrode and adapted to develop and sustain an arc discharge taking place between said auxiliary electrode and'one of said main electrodes so as to ensure that before the contacting of said main electrodes said auxiliary electrode is heated by the action of heat evolved therein mainly by said are discharge to a temperature exceeding that of any of said main electrodes.

2. A thermal time delay switch as claimed in claim 1, in which the direct electrical and thermal connection between the auxiliary electrode and the bimetallic main electrode is present only at one end of said auxiliary electrode.

3. A thermal time delay switch as claimed in claim 1, in which the minimum operating temperature of the auxiliary electrode is at least 600 C. V

4. A thermal time delay switch as claimed in claim 1, in which the cross-section of the auxiliary electrode is by. at least 50% smaller than the cross-section of the main electrode. 1

5. A thermal time delay switch as claimed in claim 1, in which the bimetallic main electrode is provided with a coating, due to the presence of which its work function exceeds that of the auxiliary electrode.

6. A thermal time delay switch as claimed in claim 5, in which the bimetallic main electrode is provided with .a coating of gold.

8 and are disposed in such a manner that,-on heating, they deflect in opposite directions, i. e. toward each other.

8. A thermal time delay switch as claimed in claim 1, in which the bimetallic main electrode is U-shaped and the auxiliary electrode is connected in parallel to one shank of the U.

9. A thermal time delay switch as claimed in claim 1, in which two auxiliary electrodes are provided, each of which is associated with a separate main electrode and both of the main electrodes are of the bimetallic type.

10. A thermal time delay switch as claimed in claim 1, in which two auxiliary electrodg are provided, each of which is associated with a separate main electrode and only one of the main electrodes is bimetallic.

11. A thermal time delay switch as claimed in claim 8, comprising two auxiliary electrodes, each of which is associated with a separate main electrode, one of the auxiliary electrodes being connected to one shank of the U-shaped main electrode.

References Cited in the file of this patent I UNITED STATES PATENTS 2,200,443 Dench May 14, 1940 2,284,103 Smitley May 26, 1942 2,294,203 Peters Aug. 25, 1942 2,305,223 McCarthy Dec. 15, 1942 2,330,161 Townsend Sept. 21, 1943 2,372,295 Rubenstein et al Mar. 27, 1945 2,485,520 Warsher Oct. 18, 1949 2,542,149 Lemaigre-Voreaux Feb. 20, 1951 2,601,917 Lemaigre-Voreaux July 1, 1952 

